New Polycarbonate-Based Thermoplastic Polyurethane Binder for HMX Based Explosives

Transcription

1 New Polycarbonate-Based Thermoplastic Polyurethane Binder for HMX Based Explosives Lawrence Livermore National Laboratory LLNL-PRES Insensitive Munitions and Energetic Materials Technology Symposium Portland, Oregon April 23-26, 2018 Emily Robertson LLNL-PRES-XXXXXX This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE- AC52-07NA Lawrence Livermore National Security, LLC

2 New commercially available TPUs may provide improved long-term stability over current TPUs Advantages: More thermally and hydrolytically stable than Estane 5703 Lower density compared to fluoropolymers more desensitizing Disadvantages: Limited solubility in solvents of interest Tm for hard segments tend to be above the traditional maximum temperatures pressing HMX-based formulations Before we can test these properties of interest, we need to determine if it is feasible to formulate with these new materials. New TPUs are attractive but need to be tested for feasibility first 2

3 Selected 3 PC-TPU as binders of interest Thermoplastic polyurethanes are classified by polyol and isocyanate type. Urethanes have 3 basic building blocks: 1. Isocyanate (rigid) 2. Polyol (flexible) 3. Chain extender (rigid or flexible) Known material Estane Estane 5703 (used in LX-14 and 9011) is an aromatic polyester-based TPU Potential new binders PC-TPUs Polycarbonate as the polyol Excellent hydrolysis and chemical resistance at elevated temperatures Low compression set No documented use in explosives Aliphatic and aromatic as the isocyanate Aliphatic have excellent adhesion Aromatic are known for toughness 3

4 Selected 3 PC-TPU as binders of interest 3 commercially available PC-TPU were purchased. Type Polyurethane Manufacturer Aliphatic Polycarbonatebased Polyurethane Aliphatic Polycarbonatebased Polyurethane Aromatic Polycarbonatebased Polyurethane Aromatic Polyester-based Polyurethane *TSD gives a large range of properties Chronoflex AL 75A-Q ALC-75A ARC-75A Estane 5703P [now Pearlstick 5703] Durometer (Shore Hardness) Specific Gravity AdvanSource 75A ca 1.10* Biomerics 75A 1.14 Biomerics 75A 1.17 Lubrizol 70A 1.19 Fluoroelastomer Viton A-100 Chemours 79A 1.82 Selected PC-TPUs with hardness values similar to Estane

5 First concern Is it safe? A. Compatibility test of PC-TPUs with HMX Determined by gas evolution using Chemical Reactivity Test (CRT). Binder Explosive CRT Total gas release, C Chronoflex AL 75A ALC-75A ARC-75A HMX HMX HMX 0.01 cc g cc g cc g 1 Measuring gas produced by the mixture of HMX and polyurethane and comparing it to the sum of the gas evolved the individual components. (explosive + binder) 0.75 cc g -1 + explosive + binder All three mixtures produced < 0.75 cc g -1 considered compatible All three binders are compatible with HMX 5

6 First concern Is it safe? B. LLNL s 5 small scale safety testing of 95 wt% HMX: 5 wt% binder. Binder Chronoflex AL 75A ALC-75A ARC-75A LX-14 (95.5% HMX 4.5% Estane 5703) Impact Height for 50% Reaction (DH50), cm BAM Friction kg kg kg kg Spark Ω TIL = Ω Ω TIL = Ω Ω TIL = Ω CRT Total gas release, 22 C DSC Onset/Peak 5 C min -1, C (ΔH, J g -1 ) 0.05 cc g -1 Closed: 272.6/278.1 (1722) Pin Hole: 274.0/278.8 (1734) 0.04 cc g -1 Closed: 276.6/279.9 (1783) Pin Hole: 278.2/281.4 (1741) 0.10 cc g -1 Closed: 279.0/282.1 (1605) Pin Hole: 279.3/282.4 (1624) Ω 0.03 cc g -1 Closed: 276.6/280.7 (1565) Pin Hole: 275.1/279.3 (1740) All formulations are in the same general range (which is to be expected). Main variations are in their impact sensitivity. All three binders register on the same safety scale as LX-14 6

7 Second concern Could we press to high density? LLNL has a limitation (for safety) of pressing HMX formulations at up to 105 C with in-die pressures up to 35 ksi Type Polyurethane Tg(SS) Tg(HS) Tm(SS) Tm(HS) Test Press Aliphatic Polycarbonate-based Aliphatic Polycarbonate-based Aromatic Polycarbonate-based Chronoflex AL 75A ALC-75A ARC-75A C NO 68.2 C C 98.8% TMD C C C 98.5% TMD C NO 72.4 C C 98.3% TMD Estane 5703 has a hard segment melting temperature between 150 C and 200 C, depending on the content and perfection of the crystallites 1 1. Hoffman, D.M., Dynamic mechanical signatures of a polyester-urethane and plastic-bonded explosives based on this polymer. Journal of Applied Polymer Science, (5): p All three binders have melting characteristics similar to Estane 5703 and are capable of pressing to high densities 7

8 Third concern Can we formulate it? A. Binders need to dissolve in a solvent that does not readily dissolve HMX as well to allow for coating the explosive LX-14 uses MEK to dissolve the Estane binder. Polyurethane Chloroform Cyclohexanone 50:50 MEK:Toluene Chronoflex AL 75A ALC-75A ARC-75A HMX Solubility Readily dissolves Readily dissolves Dissolves with minimal heat Dissolves with minimal heat Dissolves with heat Dissolves with heat MEK + Benzoflex 9-88 (plasticizer) No Dissolves Dissolves with high heat Dissolves with heat g/ 100 ml 1.0 g/ C g/ C 4 : g/ C g/ C g/ C 30 C 4 + Unknown 2. Yasuda, S. K. (1968). Microdetermination of estane in explosive mixtures. 3. Sitzmann, M. E., et. al. "Solubilities of High Explosives: Removal of High Explosive Fillers from Munitions by Chemical Dissolution. 4. B. Singh, L. K. C., P.N. Gadhikar (1978). "A Survey on the Cyclotetramethylene Tetranitramine (HMX)." Cyclohexanone selected for all three to reduce variability going forward No No 8

9 Third concern Can we formulate it? B. Slurry coating procedure utilized as it would be the most scalable Cyclohexanone solubility in water starts out low but increases rapidly with temperature. As such, the lacquer addition must be done at ambient (20 25 C). Incorporated HMX in water Immediately after lacquer addition Immediately after water addition Slurry reached ~80 C Resulting molding powder If lacquer was added to a warm (60 C) slurry, the binder becomes associated with the water phase and coats the vessel rather than forming beads. 9

10 Molding powder is binder encapsulated by HMX ARC ALC Chronoflex All three formed uniform molding powder 10

11 How do they measure up? Type Polyurethane Safety Pressability Lacquers Slurry Coating Aliphatic Aliphatic Chronoflex AL 75A ALC-75A Aromatic ARC-75A Similar Similar Similar Slightly lower melting point (Tm (HS) 110 C) Slightly lower melting point (Tm (HS) 133 C) Slightly higher melting point (Tm (HS) 166 C) Multiple options to dissolve Multiple options to dissolve Difficult to dissolve Similar Similar Similar All three have similar safety and pressability. Molding powders with similar particle sizes are achievable under identical parameters. The aromatic PC-TPU was very limited in solvents. The aliphatic PC-TPUs were more flexible in their solvent options. Aliphatic PC-TPUs have benefits over the Aromatic PC-TPUs 11

12 Future plans Thermal characterization Coefficient of Thermal Expansion (CTE) Softening point Thermal Mechanical Anlaysis (TMA) Explosive Characteristics Detonation velocity C-J pressure Disc Acceleration experiment (DAX) 12

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14 Chronoflex DSC ChronoFlex AL 75A aliphatic polycarbonate-based polyurethane. 20 mg tested in a closed hermetic dish from -80 C to 205 C at 5 Cmin -1 14

15 ALC DSC ALC aliphatic polycarbonate-based polyurethane. 20 mg tested in a closed hermetic dish from -80 C to 205 C at 5 Cmin -1 15

16 ARC DSC ARC aromatic polycarbonate-based polyurethane. 20 mg tested in a closed hermetic dish from -80 C to 205 C at 5 Cmin -1 16